and the IEC 60255 IDMT Reset equation is:
where:
● t
op
is the operating time
● t
r
is the reset time
● T is the Time Multiplier setting
● M is the ratio of the measured current divided by the threshold current (I/Is)
● β is a constant, which can be chosen to satisfy the required curve characteristic
● α is a constant, which can be chosen to satisfy the required curve characteristic
● C is a constant for adding Definite Time (Definite Time adder)
● L is a constant (usually only used for ANSI/IEEE curves)
The constant values for the IEC IDMT curves are as follows:
Curve Description
b
constant a constant
L constant
IEC Standard Inverse Operate 0.14 0.02 0
IEC Standard Inverse Reset 8.2 6.45 0
IEC Very Inverse Operate 13.5 1 0
IEC Very Inverse Reset 50.92 2.4 0
IEC Extremely Inverse Operate 80 2 0
IEC Extremely Inverse Reset 44.1 3.03 0
UK Long Time Inverse Operate* 120 1 0
BPN (EDF) Operate* 1000 2 0.655
UK Rectifier Operate* 45900 5.6 0
FR Short Time Inverse Operate 0.05 0.04 0
Rapid Inverse (RI) characteristic
The RI operate cur
ve is represented by the following equation:
t K
M
op
=
−
1
0 339
0 236
.
.
where:
● t
op
is the operating time
● K is the Time Multiplier setting
● M is the ratio of the measur
ed current divided by the threshold current (I/I
s
)
Note:
* When using UK Long Time Inverse, BPN, UK Rectifier, FR Short Time Inverse, or RI for the Operate characteristic, DT (Definite
Time) is always used for the Reset characteristic.
P64x Chapter 9 - Current Protection Functions
P64x-TM-EN-1.3 197
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